1. Field of the Invention
The present invention relates to an on-vehicle AC generator driven by, for example, an internal combustion engine and, more particularly, to a stator structure of an on-vehicle AC generator mounted on a vehicle such as automobile or truck.
2. Description of the Related Art
Generally, in a conventional stator of an on-vehicle AC generator, an iron core (core) of a predetermined laminate length (i.e., a predetermined thickness in laminating direction) is made by laminating steel plates each of which is approximately 0.5 mm in thickness; a large number of slots opening toward a rotary shaft of the rotor, which are located inside an inner circumference of the stator, are provided; and a variety of windings, which comply with specification of the generator, are accommodated within the mentioned slots.
Furthermore, for example, as shown in FIG. 3 of the Japanese Patent No. 3256696, configuration of a stator iron core (also referred simply to as core) is cylindrical, and slots, which include openings toward a center, are provided circumferentially on the inner surface side of f the stator iron core.
Since a non-slot portion, being an outer circumferential portion of the tubular stator iron core (core), (i.e., slot bottom portion, and also referred to as core back) needs only to possess thickness for a magnetic circuit, the non-slot portion is not constructed to have so large thickness. Moreover, the whole structure is of a sheet laminate in axial direction of the stator iron core (core), and therefore it is sometimes the case that the stator iron core is fragile under the force in radial direction.
In particular, this problem is outstanding in a stator that is provided with a larger number of slots with substantially the same outside dimension of the core.
However, a support portion in order to cause a bracket serving as a casing to firmly support the stator is usually a part (e.g., outer circumferential portion) of the stator iron core (core), and accordingly a force is applied directly to the stator iron core (core) at least at the time of assembling.
When the end portion of an axial direction of the stator iron core (core), which is formed into a cylindrical shape by laminating steel plates, is fitted to an inner circumferential surface of a bowl-shaped bracket, a deformation force in radial direction and a force in a direction of stripping off a laminate layer at the shaft end of the stator iron core (core) is applied to the stator iron core (core).
Further, in the case of a stator iron core in which an end portion of the stator iron core (core) is provided with by step for sufficient fitting, the core back is made even smaller in thickness, and the increase in degrees of deformation is conceivable as well.
On the other hand, conventionally, an insulating resin that is provided at a portion (i.e., coil end) of a stator winding (also referred simply to as coil) protruding from the stator iron core (core) has its primary object to provide insulation from the other parts. Therefore, the insulating resin is provided just for thinly covering the surface of the strand.
Further, the insulating resin is provided (applied), being intended to ensure insulation between the stator winding (coil) housed in a bundle within a narrow slot and the stator iron core (core). In some cases, the insulating resin just adheres secondarily to the coil end, and not all the coil ends are covered with the insulting resin.
The Japanese Patent No. 3256696 discloses an insulating resin covering the whole coil ends of an aligned continuous winding.
This art intends to uniformize heat radiation of a coil end. There is no detailed description concerning a state of resin in the coil end, the state of the core end portion, a state of resin within a slot or the like.
Although it is disclosed in this prior art that a component having a higher thermal conductivity than a base resin is mixed into a base resin as an insulating resin, this disclosure relates to the heat radiation toward an outer perimeter surface of the coil end. There is no disclosure regarding correlation between the insulating resin and the end support portion of the stator iron core (core).
In addition, the mentioned aligned continuous winding means “winding manufactured in the following way. A plurality of windings are prepared each of which is made by folding a continuous strand outside of the slot on the side of both end faces of the stator iron core (core) and winding about the slots so as to get through alternately inner layer and outer layer in depth direction of the slot within the slots for each predetermined number of slots. This plurality of windings consists of at least one set of winding group formed by folding at the same time plural strands. Further, the winding group is aligned at a pitch of a predetermined number of slots so that straight-line portions may be connected with a turn portion.” (See Paragraph 0015 of the Japanese Patent No. 3256696)
Moreover, the Japanese Patent Publication (unexamined) No. 218695/2002 discloses ratio of the winding conductor and the insulating resin occupying in axial cross sectional area of contour of a connecting part (circumferential connection part) of a part extending from the core of the coil end. It is also disclosed in this prior art to intend improvement both in rigidity of the whole stator and in cooling capability of the stator winding (coil).
Further, the Japanese Patent Publication (unexamined) No. 218405/2001 discloses an insulating resin having a high vibration damping factor, achieved.
Likewise, the Japanese Patent Publication (unexamined) No. 255140/1995 discloses an art in which a resin possessing a predetermined elastic characteristic is provided between coil strands and/or between iron core and coil. It is also disclosed in this prior art that a damping factor of vibration is made high by increasing rigidity of an excitation portion (especially, stator iron core) thereby achieving reduction in electromagnetic noise.
Further, the Japanese Patent Publication (unexamined) No. 119883/2001 discloses a resin provided to fill up gaps at the coil end, being a conductive segment. It is intended in this prior art to achieve improvement in cooling capability by performing a forced-cooling with cooling means, as well as to ensure insulation performance and withstand pressure to earthquake, and reduction in wind noise.
The Japanese Patent Publication (unexamined) No. 119883/2001 discloses a manufacturing method in which a resin is mounted on the coil end by fluidized dipping, thereby easy control of interface and easy working are achieved. Any internal state of the slot, however, is not explicitly described in this art.
On the other hand, in a conventional laminate core made by laminating steel plates, coil is inserted into slots, and thereafter a rustproof coating is applied to the entire surface of the coil thereby achieving reliability and durability at the time of being mounted on the generator.
For fitting such a laminate core to the bracket, in one method, an inner circumferential surface of the bracket is fitted to an outer circumference of the laminate core in the state of having been coated with a rust inhibitor; while in another method, fitting is performed after both end portions of an axial direction of the laminate core is machined by step machining for positioning of the fitting.
In the former method, the inner circumferential surface of the bracket is fitted to the laminate core while the portion, which is coated with the rust inhibitor, of an axial end of the outer circumference of the core is being chipped off to some extent.
In the latter method, a place of the laminate core, to which axial end portion of the bracket is fitted, has been preliminarily chipped off toward inner circumference side, and a base of the steel plate on an axial surface and on a radial surface is exposed forming an L shape.
Although dimensional fitting of both members is easy, the bracket applies a fitting force to the laminate core in the exposed state, and therefore stripping-off one laminate from another is likely to occur. In this case, the laminate core is easy to corrode.
Actually, a problem exits in that water is likely to be retained at the boundary between the machined portion of the core axial end and the fitted portion of the bracket, and the stator (core part) is enlarged toward the axial side due to spread of rust at this boundary portion eventually locking the rotor rotating inside the inner circumference.
As described above, in the conventional stator for a on-vehicle AC generator, any rigidity of stator conforming to a support structure (bracket) is not ensured, and a rigidity to be performed by a support portion of the axial end surface of the core (that is, end surface portion of the core to be fitted to the bracket) is low. Therefore, deformation at the time of press-fitting the core in axial direction of the bracket (i.e., fitting to the bracket) may occur at the time of assembling, or stripping off the laminated steel plates, slip of the laminates or the like may occur. As a result, a further problem of poor withstand pressure or corrosion is easy to occur. Moreover, a problem exists in that any electromagnetic noise due to deformation is increased.